Ecological Basics

Ecology is the biological science concerned with understanding the interplay between organisms (biological or biotic factors) and their environment (abiotic factors). As such, ecology combines skills from many different disciplines including geology, chemistry, biogeography, botany, zoology, physiology, and even economics. Despite the diversity of skills and background knowledge, there are several key concepts which help ecologists understand the world around them.

The niche is best thought of as the fit of an organism with its environment. Niche is distinct for each species and is defined as the unique set of resources used by members of the species. Niche is usually broken into two categories. The fundamental niche includes all areas that an organism might inhabit in the absence of other factors like competitors, predators, and unusual abiotic conditions like flooding or drought. Normally, a species does not exist in a void but rather competes with other species and may be exposed to random environmental events that it cannot survive. The subset of the environment where the organism actually survives, grows, and reproduces is termed the “realized niche”. Part of what defines niche is the organism’s ecological role in the environment.

All organisms require energy for maintenance, growth, and reproduction. Some organisms like plants and algae attain their energy directly from sunlight. These organisms are referred to as “autotrophs” and they form the base of the food chain. Most other organisms obtain their energy by eating autotrophs (herbivores) or by eating other animals (predators). Recyclers are sometimes called saprophytes or detritivores and they are important in the process of organic break down of dead or decaying materials. Mushrooms are saprophytes. Parasites feed on other organisms and weaken them but do not cause death. Parasitoids are specialized insect parasites that cause the death of their hosts.

At some level, all organisms compete with other organisms in their environment. Ecologists are concerned with two types of competition: interspecific and intraspecific. Interspecific competition refers to competition between species. A good example of interspecific competition is when multiple species of plants live in close proximity. Because light is the source of energy used to make sugars and because light is a limiting factor for growth in many plants, plants that are overshadowed by their neighbors often fail to establish or soon wither and die. A second type of competition takes place between members of the same species and is termed intraspecific competition. Intraspecific competition takes place within a niche and often can be thought of as an individual’s scramble for resources. Intraspecific competition also refers to competition for mates and explains male secondary sexual characteristics such as bright colors, large horns, complex songs, etc.

What is a species? Most biologists define a species as a population of interbreeding organisms that produce viable offspring. Unfortunately, a biological species is very difficult to define because its classification is tightly linked with its formation in response to environmental and biotic factors. A single species often occurs over a large range and because environmental conditions and biotic selection pressures differ through the range, small sub-populations often form. As these populations respond to selection pressures they adapt to their local environment and microevolution takes place. Over time, the members of a species can acquire enough differences to be distinguished from other closely-related members of the population. Once organisms can be distinguished from one another, they are usually designated as subspecies. Given more time in separation or a strong selection factor, subspecies or genetic races have the potential of becoming new species as they adapt to better fit their new niche. As the population of a new species increases, its occupation of suitable habitat becomes its distributional range. For some species which have desirable qualities for human consumption, humans impose directional selection to increase these traits. Examples include most crops (corn, apples, alfalfa), pets (horses, dogs), and livestock (cows, pigs, sheep). Directional selection is often accompanied by changes in distribution as these species are moved around the globe by humans. The combined effects of directional selection, commercialization, and agriculture can make it difficult to determine whether a species is exotic or native.

As environmental or geological conditions change, often a species’ range also changes. Biologists who are interested in species’ ranges, both past and present, are referred to as biogeographers. By comparing past and present ranges, biogeographers can determine which species are “native” and which have recently expanded their range in some manner. An "endemic" species is one which naturally occurs in a particular area and is native only to that area.